By way of introduction, it is known that there is a variety of locations of wind turbines used for the transformation of wind energy into electric power, which are located in strategic areas unprotected from physical obstacles for the purpose of maximising wind energy, for instance, hilltops, offshore areas, etc.
This location in exposed areas and the itself geometry of wind turbines, which corresponds to a pole anchored on its basis to the ground, and in the upper part has a hub from where leave three or more blades of aerodynamic profile; it makes that the probability of attracting lightning is high and, once the lightning reaches the wind turbine, a high-magnitude current runs through it, that can impair the inner components of the wind turbine, with the subsequent damage for the energy supplying company, and the risk involved for the operators from replacing said impaired parts in position situ according to the extreme locations of the wind turbines. The most critical point of lightning transmission to ground occurs when the lightning falls on the moving blades and the lightning must be transferred to the nacelle of the wind turbine that remains static, so a binding element must be positioned between the moving blades and the static nacelle, which transmits said lightning to ground and does not affect the normal blade performance.
To solve this problem, a system protecting the components of the wind turbine against lightning strikes is known, which consists of directing discharge from the blade tip or blade to ground, using first an internal wire joining the blade tip, supported on the internal stiffening beam of the blade to subsequently lead this electrical current to the hub through the blade bearing and from there to the low speed shaft. Then the frame is reached through the bearings and, finally, crossing the slewing ring joining the frame to the tower, the discharge is taken to the ground. However, this solution shows the major disadvantage that the lightning discharged by this way damages the bearings and discharge train, so alternative solutions have been searched for.
With this regard, to be noted is the patent application also of this applicant, under publication number ES-2265776, which describes a lightning transmission device, which is formed by a conduction bar fixed to a second insulating bar, and fixed to a wind turbine hub. Therefore, a first end of the lightning transmission device is in front of a metal strip located at the root of each blade of the wind turbine at a first distance which allows an electric jump of a lightning incident on a blade tip of the wind turbine, while a second end is in front of a gutter of a nacelle of the wind turbine at a second distance which allows the electric jump of the lightning. Therefore, the lightning runs from the blade tip at which it is incident thereon to the ground, through a number of conduction means including the lightning transmission device, said means preventing the lightning from affecting the sensitive parts of the wind turbine.
This solution ensures the non-impairment of the main components of the wind turbine, but shows an inconvenience related mainly to the assembly and installation of said lightning transmission device with respect to the blade and the gutter; as for the lightning transmission onto the ground to be performed optimally, predefined, specific distances must be ensured between the ends of the conductor bar and the blade strip and the gutter, respectively, without direct contact between them; for this, the transmission device must be placed with a lot of precision, as if the distance between the metal strip of the blade and the end of the bar, or between the other end of the bar and the gutter is excessive, the tension required for the electrical arc to be triggered increases between them and can stop working adequately, and the arc will jump to other metal elements close to the wind turbine, with the subsequent problem involved by this. This distance is also affected by the factory tolerances of the blade and the gutter.
It must be noted that there are also lightning transmission devices with direct contact between the blade (turning over its shaft and also turning with the hub) and the gutter (static), but these generate welding problems when a high current runs through it, generating excessive noises due to rubbing between components, in addition to requiring frequent maintenance due to wear for the friction between mobile and fixed parts.
Therefore, given the existent inconveniences during assembly and guarantee of the predefined distances for the electric arc to jump between the metal strip of the blade, the conductor bar, and the gutter, a new lightning transmission device is necessary to be installed in any type of wind turbine, which enables adaptability to the variability in the distances existing between the metal strips of the blades and the gutter element, and ensuring at all times the adequate electrical conduction between both elements when a lightning reaches the structure of the wind turbine through the respective blades thereof; and all of this with a simple transmission device, easy to install and maintain, and economically competitive with respect to the state of the art known to date.